The invention refers to a nano granular material (NGM) comprising electrically conducting nano crystals embedded in an insulating matrix and surrounding layer. The material carries a high current density by variable range hopping, of electrons between the nano crystals.
U.S. Pat. No. 6,246,055 discloses a nano granular material as well as a photon detector made thereof, which delivers at low light photon quantities and energies usable for signals. The photon detector is partly composed from a nano-crystalline phase and is included in an insulating carbon matrix and which is producible with simple production machines and processes. The production of similar materials using organometallic precursors is described in: H. W. P. Koops, A. Kaya, M. Weber. “Fabrication and Characterization of Platinum nano crystalline Material Grown by Electron-beam Induced Deposition”, J. Vac. Sci. Technol, B 13(6) November/December (1995) 2400-2403. High resolution Transmission-electron microscope image at 200 kV reveals 12 to 14 lattice planes of the platinum or gold single crystals of 0.408 nm distance. 800 to 1000 atoms form a perfect crystal embedded into a Fullerene matrix.
Crystal sizes are for Au/C: 3-4 nm obtained from Dimethyl-Gold-Trifluoro-Acetylacetonat, and for Pt/C: 1.8-2.1 nm deposited from Cyclopentadienyl-Platin-trimethyl. [J. Kretz, M. Rudolph, M. Weber, H. W. P Koops, “Three Dimensional Structurization by Additive Lithography, Analysis of Deposits using TEM and EDX, and Application for Field Emitter Tips” Microelectronic Engineering 23 (1994) 477-481]
However, there the matrix in Au/C and Pt/C materials is from Fullerene and presents a 2-D resistor surrounding the NGM material having a Fullerene matrix. This matrix is over the time of use etched away by water and activated gas ions. This limits the lifetime of the detector.
It is desirable to have a nano granular material with extraordinary properties like high current conductivity and radiation sensitivity with a long lifetime.
According to an aspect of the invention this task is solved by high current density carrying nano granular material comprising conducting nano crystals embedded in a matrix, wherein the matrix consists of insulating carbon-free material. Preferably the insulating material is an oxide, oxy-nitride or nitride. Even semiconductors can be used if they are insulating by surface depletion by their small layer thickness.
This invention is strictly different from the one taught in e.g. US Photo detector patent U.S. Pat. No. 6,246,055 B1. There the nano crystalline material is produced from organometallic precursors and has a carbonaceous matrix of low conductivity. Such a material is destroyed by a reaction of the carbonaceous compounds in the matter and in the surrounding surface, which takes place in the presence of excited water or gas atoms which are delivered from the environment and excited by the electromagnetic radiation, which is to be detected.
The carbon-free matrix and coating prevents in an advantageous way the destruction of the current leading wire or sheet, switch, photo detector, or solar cell due to reaction with surrounding materials like water or atmospheric gases, which are excited by the impinging energetic photons.
The material according to an aspect of the invention enables many applications and new electrical components, whereby a separation between the nano crystals is smaller than 2 nm. If required in particular cases the separation can be made larger, e. g. up to 5 nm.
In a preferred electrical component the material is shaped as a thin layer, having an entrance plane for radiation and electrodes for applying, an electrical field to the material.
In one embodiment of this inventive component said electrodes are electrically connected to the material. Such component can be used as detector for visible light, ultraviolet radiation or X-rays.
In another embodiment of this inventive component said electrodes are electrically insulated from the material and further collectors are electrically connected to opposite edges of the material. Exited by a weak electrical field provided by the insulated electrodes incident light causes the electrons to flow to one of the collectors at d the holes to flow to the other one of the collectors. Therefore this embodiment is a high efficient solar cell. Detailed explanations follow in connection with the drawings.
In another electrical component comprising material according to an aspect of the invention the material forms field emitter tips being arranged in vacuum cells which are formed by two planes, at least one of which is transparent for photons, and spacers between the planes, the transparent plane is covered with a luminescent layer in each cell, said field emitter tips are arranged opposite to the luminescent layers and the spacers carry an accelerator grid. This component generates light very effectively.
In a further development of this electrical component said cells form groups having luminescent layers of different colors within each group. This enables different colors of the light at the application as a light source e or as a display, if said field emitter tips or groups of said field emitter tips can be activated separately from each other.
To improve focusing of the emitted electrons in this electrical component an extractor can be attached to each of said field emitter tips.
A further embodiment of the electrical component can serve as radiation detector wherein the material forms field emitter tips which are arranged on a transparent support plane with tip structures and wherein the field emitter tips emit electrons which occupy the excited excitonic levels being lifted to those energy levels by incident photons of IR-, visible-, or X-radiation due to the extraction voltage between the emitter tips and a micro channel plate and co-act with a charge detector array through the micro channel plate.
Another embodiment of the electrical component forms a high voltage and high current switch, wherein the material forms an array of field emitter tips being arranged as cathode at one end of a vacuum tube and wherein the vacuum tube comprises further an anode and near the cathode an extractor. Preferably the extractor is arranged co-planar to the cathode or below (opposite to the anode) an insulating layer carrying the cathode and is used to switch the emission with a low voltage. This embodiment can further be improved by at least one accelerator dynode.
In an advantageous method for manufacturing material according, to an aspect of the invention a high energy electron, ion or photon beam is directed on a sample producing secondary electrons, wherein multiple inorganic molecules and metallic precursor gas are supplied, which are dissociated by said secondary electrons resulting in the deposition of the insulating matrix and metallic nano crystals embedded therein.
An arrangement for manufacturing material according to an aspect of the invention comprises in a vacuum chamber an electron, ion or photon beam source as a deposition system and a computer controlled multiple inorganic molecules and metallic precursor gas supply system.
An arrangement for manufacturing electrical components according to an aspect of the invention with areal field emitter tips comprises in a vacuum chamber an electron, ion or photon beam reducing image projection systems as a deposition system having a computer controlled multiple inorganic molecules and metallic precursor gas supply system in a structured fashion to define areal arrangements of field emitter tips.
The invention, according to an aspect thereof, relates further to an arrangement for manufacturing elongated forms of material according, to an aspect of the invention, which comprises in a vacuum chamber an electron, ion or photon beam source as a deposition system and a computer controlled multiple inorganic molecules and metallic precursor gas supply system and comprises further a transport system for the elongated material in order to move the material through a reaction area. Preferably this arrangement comprises means for maintaining temperature of the material in the reaction area. This solves the problem to deposit large areas of the NGM Material.
Another arrangement for manufacturing material according to an aspect of the invention by electron, ion or photon beam shadow mask image projection system uses a deposition system having a computer controlled multiple precursor gas supply system and the anode drop of a gas discharge areal energy source to deposit in a structured fashion NGM material for arrays of field emission electron or ion sources, for sheets, for long wire deposition, for power cables, for multiple pixel aerial photon detectors, for fast imaging in the IR, visible and X-ray regime, as well as for solar cells. For the purpose of enlarging the area this arrangement can be improved further by an electrostatic or magnetic multi beam deflection capability.
Another advantageous method for manufacturing nano granular materials according to an aspect of the invention uses especially tip arrays replicated with nano-imprint lithography means and then supplied with field emitter tips by high field material deposition using a deposition system having a computer controlled multiple precursor gas supply system, with the refined method of measuring the electron field emission by a computer evaluation of the emission on current during the tip growth process in an intermediate step in very short times compared to the tip growth process and to stop the growth for all parallel growing tips by a computer evaluation of the emission at a defined emission current.
A further development of this method is characterized in that the intermediate measurement of emission characteristics presents also a method to renew all tips by using a deposition system having a computer controlled multiple precursor (more than 1) gas supply system also equipped with halogens to etch all tips in the large area emitter structure and to re-grow the tips to the previous perfection with the high-field chemistry 1, 2 or 3 molecule deposition process.
Such process per se is published in:    M. Bischoff Int. Journal of Electronics 1992, Vol. 73 No. 5, 827-828    H. B. Linden, e. Hilt, H. D. Beckey, J. Phys. E: sci. Instruments. Vol 11 1987 1033 “High rate growth of dentrites on thin wire anodes for field desorption mass spectrometry”    J. T. L. Thong “Metallic Nanowires grown via field emission induced growth as electron sources” IVNC 2013 Tech digest 1 21 page 94.
In the following the matrix of the inventive material is referred to as M, e. g. Au/M means gold nano crystals in such matrix.
The invention, according to an aspect thereof, enables material for high current conducting wires and sheets, for bright electron and ion sources, as well as for photon detectors. The task is solved, using an energetic electron impact process, which produces the material fabricated as a nano-crystalline material, which is composed from conducting metal- or metal compound nanocrystals embedded into an insulating oxide, oxinitride or nitride matrix, which also surrounds the material with a non-conducting oxide, oxinitride or nitride layer, or by a semiconducting material which is in its surface states depleted by the small geometry. The nano crystals are having a dimension of smaller than 15 nm diameter and the intermediate insulating layer is thinner than 2 nm between the nano crystals, which is the reason for single charge moving from nano crystal to nano crystal using excited excitonie surface orbital states, which overlap to the ones of neighboring crystals and therefore free electrons and holes can form Bosons which are distributed through all the NGM material.
By the effect called Bose Einstein Condensation (BEC) positive and negative charges can form Bosons, which allows the condensation of many Bosons in one energy level. This is the reason for the very high current densities emitted from field emitter tips and being carried in thin wires at room temperature without destruction. (Literature: L. V. Butov et. al. “Towards Bose-Einstein Condensation of excitons in potential traps” in: NATURE/Vol. 47/47-52, 2. May 2002). Typically metals or metallic compounds have no bandgap in their energy level structure, and therefore cannot present Eigenstates of distinct separation to absorb energy from photons. Si has a bandgap of 1.5 eV and can therefore absorb electromagnetic radiation energy quanta with this value. That leads to ca. 16% effectivity in Si-solar cells in the visible spectrum collecting energy from the sun.
In addition the geometry quantization of the nano-crystals, which have a diameter below 10 nm, prevents that high energy phonons, like in 3-dimensional electron gas materials, like normal crystalline metals or metal alloy conductors, can be excited.
This is due to the fact that inside the nano crystal only 8 to 12 lattice planes exist. The insulating matrix having, a different density than the crystal materials also prevents the impulse transfer to neighboring atom chains. According to Patton and Geller only the lower energy state for acoustic phonons is occupied, which has an energy of 2 meV corresponding to a temperature of 23.2 K or −250° C. (Patton, K. R. & Geller, M. Phonons: in “A nanoparticle mechanically coupled to a substrate”, Phys. Rev. B 67, 155418 (2003).
Therefore photo detectors from such materials do not need an additional power consuming Peltier cooler to reach the detection limit at 8 μm photon wavelength (for the Au/M compound or 4 nm crystal diameter), like commercial infrared cameras need to have.
Due to the fabrication method with an energetic electron impact on adsorbed molecules many for semiconductor photo-detectors required technology fabrication steps are avoided which makes the production of NGM current leads and detectors much cheaper.
Very small amounts of the compound material are sufficient to detect photons. In earlier experiments to measure the effectivity ala photon detector from Au/M deposited from Dimethyl-Gold-Acetylacetonate with the dimensions of 2 mm×50 nm wire width and thickness showed at illumination with a lamp of 60 W power a photocurrent of several nA. Resistive change was 10 MΩ to 3 MΩ. A Voltage change by 2 meV is good for 12 bit image contrast at 1 μV amplifier noise level.
Aerial detectors of 2 μm×2 μm deposited from Pt/M material showed similar results. Recently (not published jet) we measured from Pt/M wires of an area of 0.32 μm2 an photocurrent of 200 nA illuminating the area of the structure with a power density like the sun sends to the earth of 100 mW/mm2. The solar light source delivers to the earth 1.36 kW/m2=1.36 10{circumflex over (0)}3/10{circumflex over (0)}4 W/cm2=0.136 W/cm2=136 W/cm2, which is 100 times less than the laser source intensity of our experiment.
Therefore the efficiency of this material, if produced in an aerial coating, would allow converting the energy from the sun with a so far not reached efficiency!
An experiment revealed: red light of 700 nm wavelength (=1.3 eV per quanta) with an intensity of 100 mW/mm2 releases, if used with an intensity of 100 mW/mm2 from the deposited area of 3.2 10{circumflex over (0)}-9 cm2 an electron current density 0.2 μA/3.2 10{circumflex over (0)}-9 cm2=2 10−7 A/3.2 10{circumflex over (0)}-9=60 A/cm2=60 A/cm2. With a voltage difference of 0.12 V this would amount to 60×0.12 W/cm2=7.2 W/cm2 collection efficiency of the Pt/M material. With the solar light source of 136 mW/cm2, which is 1/100 of the experimental condition the NGM Material would have collected 72 mW/cm2. This is a significantly higher value (around 3), than Si solar cells, which convert 15% of this energy, which is 20.4 mW/cm2, when using only yellow to blue light. NGM Pt/M materials efficiency in monochromatic red light is at least a factor of 3 higher than that of Si-solar cells.
Producing the nano granular material with a larger grain size would increase the number of electrons, which are excited by the photon and can tunnel through the NGM material, due to the effect of the reduction of the Eigenstate separation values of the electron orbitals at the crystal surface.
A crystal diameter of 2 nm correspond to an Eigenstate separation of 125 mV, 4 nm to 65 eV, 6 nm to 32.5 meV and 8 nm to 16 meV, which would correspond to a 100 times higher effectivity for electromagnetic radiation conversion compared to silicon or similar solar cells!
Therefore it is a task for the production of the crystals to select the deposition and materials composition conditions in a way that larger crystals are produced in the deposit. This can be achieved using additional reaction partners, which reduce the confining molecules which form the insulating matrix.
For hopping conduction it is necessary that the crystals have a separation from each other which is as small as <2 nm. However, if there is a separation larger than 2 nm, and no hopping conduction is possible, such materials are insulators. One method is to use a gas discharge with ions as it is used to coat tools e.g. with a hard layer of AlTiN with an amorphous Si3N4 insulator matrix material. [Lecture of H. Frank G F E at 3rd ITG Workshop on vacuum nano electronics at Bad Honnef 19.8.12] The crystals and intermediate oxide or nitride fit the expectations. However, the violet looking materials layers have not been investigated for optical and electrical activity so far.
Another method is to use a multi-source sputter deposition system with material flux control.
Another method is ALD Atomic Layer deposition with Multi-precursor reactions for conductive nano crystals and insulating embedding of the crystal grains in a repeated manner to form NGM material layers of several 100 nm thicknesses.
Another method is to use the as discharge in a large flat chamber to generate fast electrons with the anode fall for electrons to decompose and deposit to a target the adsorbed mixture of inorganic precursor molecules of several compounds as supplied to the gas phase in the discharge. Appropriate inorganic low vapor pressure compounds are the fluorines, or halogenes of Al and Ti, as well as Si. Also other compounds forming mixtures of conducting crystalline material from metals and nitrides or oxides can be used, but they must be selected with their condensation reaction energy which avoids, that they co-condense in an epitaxial way with the insulating phase which is embedding the nano crystals phase.
Typically the crystallographic system of the deposits of the compounds of the crystal core and the surrounding insulator should not match, and for the insulating phase a hindered epitaxy is needed which has an epitaxial temperature below the temperature of the crystals growing temperature.
Another way to fabricate the NGM materials in large areas is to use focused electron beam induced deposition using massive parallel electron beams from gas discharges, thermal source arrays, Thermofield electron source arrays or field emitter arrays produced by semiconductor technology and micromechanical means, especially using tip arrays replicated with nano imprint lithography means and then supplied with field emitter tips by high field material deposition.